White light lamp



3m. 13, 1942. s ISENBERG 2,269,81

WHITE LIGHT LAMP Filed Aug. 17, 1938 Jail 507v fife/2,5659 3 4120; ifs/W Qyiiiom (3 5 Patented ,Jan. 13, 1,942-

WHITE LIGHT LAMP Sampson Isenberg, Chicago, 111., assignor to General Luminescent Corporation, Chicago, 111., a corporation of Illinois Application August 17, 1938, Serial No. 225,351

1 Claim.

My invention relates to the production of white light by the use of means and methods whereby the efiiciency of the emitter means expressed in lumen over watts is greater than can be obtained by the use of any present commercially available sources of white light.

It is well known that light produced by the incandescence of a tungsten or similar filament is the commonest form of light in use at the present time in the so called civilized countries. While the incandescent light is much more efiicient than other forms of light which have been employed for illuminating purposes, it is well known that only a relatively small amount of the energy input becomes available for illuminating purposes, that is, only' a relatively small proportion of the energy is converted into radia tions falling within the visible spectrum. The same general statement is true of all present commercial illuminating devices, except that in these other cases, e. g., in the case of the gas burner, the efficiency usually is still less than in the case of the incandescent filament lamp. Because of this low efllciency, as well as for other reasons, many developments have had for their purpose to increase the efiiciency of light emitters. For example, incandescent lamps have,. in the past, been improved in eiliciency, first by the selection of improved filaments (for example, substitution of tungsten for carbon), and then by increasing the temperature of the filament. Concerning the latter, improvements have been made in the direction of using inert gases under pressure within a bulb housingthe filament so that the temperature of the filament may be raised without appreciable [volatilization of the substance thereof.

It has been well known for some time that light generated by fluorescence of certain types of materials is produced more efilciently than the light of an incandescent filament, primarily because the fluorescent material has the property of converting the energy of short wave lengths invisible to the human eye into radiations in the visible spectrum. Accordingly, investigators in this field have given some thought-to the production of awhite light by the utilization of the general principles involved in the excitation .of fiuorescent or luminescent substances. The investigators have been concerned primarily with the discovery of a material which will become luminescent when excited and produce a substantially white light, that is, a light so nearly resembling the white light as to satisfy most general requirements. Heretoiore, however, all practical results in this direction, so far as I am aware, have been confined to the production of so-called luminescent tubes used in sign work and the like wherein the color emitted represents visible radiations of only a part of the visible spectrum, so that the emitted rays appear either green, red, blue, or some variation of true reds, greens and blues.

The principal object of my invention is to produce an improved white light.

Another object is to produce a truly white light in which the efiiciency expressed in lumen over watts is much greater than in other illuminating devices heretofore employed.

A still further object is the provision of practical means for and methods of utilizing the fluorescent properties of materials for the purpose of producing a white light.

Other objects and specific features of my invention will appear as the description of the invention progresses.

In carrying out my invention, I utilize a plurality. of luminescent materials, each material alone producing rays in the visible spectrum which, taken alone, would normally give the impression on the retina of a pronounced color. These materials are so combined together, how- 'ever, that at least the major radiations found in the visible spectrum are present in substantially the proportions found in so-called white light.

I may accentuate certain wave lengths to substantially imitate the characteristics of conventional artificial light sources, such as the incandescent filament, or the Welsbach gas mantle. I may, however, give greater prominence to the radiations appearing near the short end of the visible spectrum in order tomore perfectly simulate true daylight than has been possible with other forms of artificial illumination.

The general features of my invention may be embodied in various types of apparatus, and in the drawing I show certain forms of the invention, wherein Fig. 1 is an elevational view, partly broken away, showing one form which the invention may take;

Fig. 2 is a sectional view showing another embodiment;

Fig. 3 is a sectional view taken on the line 33 of Fig. 2; and

Fig. 4 is a fragmentary elevationalview showing still another embodiment.

A feature of my invention is the utilization of separate materials which become fluorescent to separately produce the three cardinal colors, using these separate materials together in suitable proportions, as will be explained, for the purpose of producing a substantially white light, and utilizing, in addition to the three cardinal colors, selected auxiliary fluorescent substances designed to supplement the radiations of the three cardinal colors and more perfectly cover substantially the entire visible spectrum, or such portions thereof as the results sought show to be desirable.

I have approached the invention from the standpoint of analyzing the visible spectrum of the source of light sought to be reproduced, and then so selecting and combining a plurality of fluorescent materials as to substantially duplicate the visible part of the spectrum so analyzed. In carrying out my invention, I combine or associate the selected fluorescent materials in accordance with several embodiments, some of which will be explained and others of which will be suggested hereinbelow.

In accordance with one form of the invention, I select three fluorescent materials which, taken alone, produce the colors, red, blue and green, respectively. I supplement these colors with auxiliary emitters, for example, small amounts of substances which, when suitably exited. become luminescent in the yellow, violet and orange portions of the spectrum. These materials are then mixed together, preferably in quite finely subdivided form, and coated on the inside of a suitable lamp designed to produce a source of energy such as in the form of radiations of relatively short wave length, for example, in the ultra violet range. Such a lamp may be, for example, a cathode ray lamp, or a lamp of the glow-discharge type, utilizing spaced electrodes between which a mixture of mercury, helium and argon is disposed, which mixture, when excited, produces a radiationefiective to cause the layer of mixed fluorescent materials on the inside of the lamp to glow and produce a light, the combination of the radiations from the different substances having the effect of white light. This form of the invention, employing any suitable source of energy to produce luminescence, has high emciency and may be produced to emit very satisfactory commercial resultant white light when the range of fluorescent materials employed is suitably selected.

As previously stated, methods for determining the wave lengths of various radiations may be determined by means known in the art. By proper selection, the total range covered by the visible spectrum (roughly 370 to 710 millionths of a millimeter) may be obtained when the materials employed are suitably selected, both quantitatively and qualitatively. Various means, some of which are known in the art, may be employed for producing a suitably thin adhesive coating of the mixed fluorescent materials onto the inside of the glass surface of the lamp, or other surfaces associated with the glass surface of the lamp.

A lamp made in accordance with this embodiment is shown in Fig. 1. In the drawing, a glass tube Hi, provided with electrodes II, has aninterior coating l2 of a mixture of luminescent materials, which layer, when excited, glows white, the brilliancy being pronounced, and the efliciency high. Excitation results from passage of an exciting current through a vaporous medium such as mercury, helium and argon, for example, which medium is usually maintained at sub-atmospheric pressure in accordance with the general practice in the glass discharge tube art. High voltage is required, approximately equal to that conventionally employed on neon tubes for advertising purposes, although some variation in voltagemay be desired. depending on features of design.

According to another form which the invention may take, substantially the same types and proportions of fluorescent materials may be employed except that in place of mixing the materials together, concentric bulbs are utilized, and the fluorescent materials or certain groups of the fluorescent materials coated separately on the inside of the concentric bulb surfaces. The coatings employed are suiliciently thin so that the radiations from an inside glass surface will pass through an outer coated glass surface with the result that the device, as a whole, when excited, gives the appearance of a single bulb which emits a white lights having a high lumen over watt efliciency.

Figs. 2 and 3 show one form of this lamp. A plurality of concentrically disposed glass or quartz or similar tubes l3, l4 and I 5 are provided, having coatings i8, ll and [8, respectively. Each tube is provided with a pair of suitable electrodes l9 and the tubes are partially filled with a. suitable excitable gas capable of gen erating waves of relatively short length when current at relatively high voltage is passed be tween the electrodes. Each tube has a difierent fluorescent coating, and the relative area is such as to produce the effect of white light.

In still another form, the surface of a lamp containing means for producing radiations of relatively low wave length for exciting the fluorescent materials is divided into relatively small areas which are separately provided with the fluorescent materials, each fluorescent material being separately applied, and the number of portions coated with each type of fluorescent material being so controlled that the proper proportion of light of the various wave lengths is obtained with the result that the device as a whole produces a white light.

This principle may be employed in several ways, as, for example, by separately coating portions of a continuous glass wall, or providing separate relatively small plates attached to a super-structure by a convenient method whereby the plates are supported on the super-structure in a position to receive radiations of low wave length from the energy emitter. In a representative embodiment of this latter principle, the structure may contain two metallic strips acting as supports and also to serve as electrodes or leads to the electrodes. The plates may be so attached as to focus on a plate at the bottom of the device. This plate may itself be coated with an extremely thin coating of fluorescent material or contain a fluorescent material such as uranium oxide. It may, moreover, be a clear glass, a transparent plastic material, or a semitranslucent material such as employed in certain types of electrical fixtures. The separate plates should be of such number as to permit flexibility in the application of the fluorescent materials, and care must be employed in taking into account the size of the device, the relative positions of the plates, the transparent plate and the electrodes. Such a device, produced in the manner described, will result in fluorescence of separate but selected materials so that the general effect is the production of a'white light delivered through the transparent or semi-translucent plate.

- the glass body-2i.

' and 2'! are adhesively or otherwise suitably secured onto an upper dome shaped portion of The inserts 24, 28 and 21, respectively, are coated with separate types of fluorescent materials, such as to produce the colors, red, blue and green, respectively, while a relatively small number of such inserts are so coated as to produce, when excited, such complementary colors as may be desired. Thus, the

total radiations from all of the coated inserts g is such as to equal in character and amount the radiation of visible white light.

Over the lower face of the glass body 2| I provide a translucent plate 28 held in positionby clips 29 secured to the glass body 2i. With this arrangement, separate colors cannot be readily detected, the plate 28 appearing true white. A suitably excited vaporous medium is provided in the body 2|, such as a mixture of mercury with other excitable gases, such as argon or other relatively inert gas or gasifiable substances. While the plate 28 may be an ordinary translucent member, it may be itself coated or contain the luminescing materials of any desired color.

As an example of a modification of a similar apparatus, I may cite the following application. The plate 28 or generally similar plate secured 'germanate; zinc telluride; rubidium urany'l nito the superstructure may be coated with any particular luminescent material. and the dome used merely as a source of ultra-violet radiation to excite the attached plate. In this manner, several colors may be obtained by using plates covered with difi'erent luminescent substances. It is obvious also that the plate 28 may, if desired, be left off, the lower portion of the glass body 2| then functioning in its place. The superstructure of the body 21 need not be transparent, or need not be formed of glass, and so it should be borne in mind that the drawing and description thereof are purely illustrative. In carrying out my invention, as previously described, the fundamental materials employed are'those which, when excited, for example by any short wave lengths such as ultra-violet light, cathode rays, X-rays, etc., produce red, blue or green emissions. Fundamentally, therefore, I employ a material which emits a red light, a

material which emits a green light, and a material which emits a blue light. The following materials are illustrative of those which may be employed for this purpose:

Red light emitters.--ZnS.Mn, ZnS.CdS, fluorescent argonite activated with Mn, fluorescent kunziteMn, fluorescent magnesite.Mn, and fluorescent cadmium phosphate.

Blue light emittera-Fluorescent caesium sulphate, leukophane, calcium tungstate, calcium molybdate, and calcium silicate.

Green light emitters.-Zinc silicate, zinc germanate, silicon sulfide, zinc sulfide, calcium zinc silicate, and zinc calcium germanate.

In the selection of complementary or auxiliary emitting substances, for example those which produce yellow, orange, violet and such colors, there is also a considerable choice. The following materials, for example, are illustrative: fluorescent zinc phosphate; fluorescent zinc sulphate; cadmium phosphate-cadmium silicate; cadmium tungstate; beryllium silicate; calcium germanate; cadmium 'germanate; zinc beryllium trate; rubidiumuranyl sulphate; boric 'acidcontaining fluorescin (approximately one millionth of a part); certain fluorescent generic organic dyes. etc. I, g

While certain of the materials given above in general. emit light of the same wave length when excited, their characters as emitters may be modified by changing conditions, for example, by

changing concentrations of materials, changing sentative instances of the use of certain of these materials are given for the further guidance of those skilled in the art: V I

As previously noted, in accordance with one form of the invention illustrated structurally in Fig. l, I combine various fluorescent materials mechanically so as toproduce in effect only a single powder-like substance which may be coated continuously onto the inside of the glass walls of a suitable lamp designed to generate exciting radiations to produce a fluorescent effect in the coating. In this form of the invention, I employ materials of'such a nature that the active centers of one material willnot be affected by the proximity of another material, or somewhat differently considered, I employ materials whose active centers are different but which will remain active when utilized in substantially the same medium. As an example, I produce a unit batch of a finished powder-like material which, when suitably employed in a lamp, will become luminescent to produce a white light. Such a powder-like material may be made up of the following constituents in the proportions indicated? The powder should be heated for a definite time at a certain temperature, depending on the crys- (a) 1 part of zinc sulfide with 0.0004 part muth .(blue).

(b)- 1 part of zinc sulfide plus 0.00001 muth (green). I

(c) 1 part of zinc-sulfide plus .004 part bismuth (red). I

Separate small batches of other fluorescent materials' are prepared as auxiliary emitting substances, and utilized as will be shown lowing paragraph:

Assuming the glass body 2| of Fig. 4 is ten centimeters in diameter and contains a total area in the 101- part bisat its upper portion of approximately 157 /2 square centimeters this area may be divided up and covered by means of 70 plates, each, having an area of about 2 square centimeters, leaving some inactive area for attachment of the plates and the location of the electrodes. Preferably using a very thin coating,'the plates are separately coated on one side and then heated to about 300 degrees C. or 400 degrees C. This promotes adhesion and, in case the fluorescent material has been deleteriously affected by grinding, it restores its activity. In the same operation, the plates, while at this temperature, may be shaped, if desired, to fit them to the superstructure iorming in the embodiment shown a part of the glass body 2|. Of these plates, 28 are coated with the red fluorescent material, 21 with the green fluorescent material, and 16 with the blue fluorescent material. 01 the remaining plates, 3 are coated with a material yielding a yellow light and 2 with a material yielding an orange light. When the plates are suitably supported and excited by cathode rays, a light is produced which, to the eye, appears to be white, that is, it combines the various wave lengths in substantially the proportions found in the visible spectrum.

In accordance with another example, I may utilize as fluorescent materials for the three cardinal colors, fluorescent calcium tungstate to obtain a blue radiation, synthetic willemite for a green radiation, and fluorescent magnesium sulphate for producing a red radiation. The proportional area of these materials utilizedis as follows: Approximately nine percent of the total area is covered with fluorescent material substantially equally divided between yellow, orange and violet. The remaining area is divided between the red, blue and green fluorescent materials, on the basis of 100, on approximately the following basis, depending on specific conditions: red, 40% to 45%; blue, 23 to 26%; and green, 30% to 34%.

The embodiment of separately coating portions of the total area, preferably the use of a plurality of separately coated, relatively small plates is particularly effective in producing desirable results. In this form, while no separate portion 2,2ee,a19

of the lamp produces a white light, but rather a colored light depending upon the materials used, and to some extent the conditions of excitation, the combination may be made to produce a true white light, wherein the proportions of the different radiations is so combined as to produce the exact effect desired. The emphasis may be placed, if desired, on certain wave lengths to produce a light which, while substantially white, has an overtone of say green, yellow, orange or the like, depending on the conditions in which the light is used and the efiect desired, by the user thereof. When I speak of white light, therefore, it is to be understood that I include, in addition to substantially colorless light, also light which, although substantially white, may possess certain wave lengths which are slightly accentuated. In this connection, it may be noted that by suitable conjoint use of only properly selected red, blue and green fluorescing materials, a light approaching in appearance true white light may be produced.

I have described my invention in detail, and i have described certain specific embodiments thereof, but the invention is limited only by the scope of the appended claim.

What I claim as new and desire to protect by Letters Patent of the United States is:

A lamp adapted to emit a white light, said lamp comprising a lower portion adapted to pass light, an upper portion carrying a combination of materials adapted then to produce at least a major proportion of the radiations found in the visible spectrum, said upper portion including a plurality of members presenting a generally smooth surface of small area, each of said surfaces being'coated with a single fluorescent material, and the number of surfaces coated with the diflerent materials being such that together 

